lecture06 - EE 338L CMOS Analog Integrated Circuit Design...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
S. Yan, EE 338L Lecture 6 1 EE 338L CMOS Analog Integrated Circuit Design Lecture 6, Single-Stage Amplifiers (3) Cascode Amplifiers We will cover different cascode amplifiers, including 1. Simple cascode amplifier 2. Multi-level cascode amplifier 3. Gain boosted cascode amplfier 4. Folded cascode amplifier 1. Simple cascode amplifier M1 M2 v out v in Vdd I B V B Large signal behavior (Vin fixed to V G1 , Vout (V DS ) sweeping from 0 to 3V) I D,CASCODE I D,SIMPLE I D V DS I II III V G1 M1A I D,SIMPLE V G2 M1B M2B V G1 I D,CASCODE Region I: M1B and M2B both in triode; Region II, M1B in saturation, M2B in triode; Region III, M1B and M2B both in saturation
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
S. Yan, EE 338L Lecture 6 2 Small signal analysis We will calculate small signal i) output resistance, ii) transconductance (when output is shorted to a fixed DC voltage), iii) DC voltage gain (when the output is open). i) Output resistance We have derived earlier, [] 2 1 2 2 2 2 1 2 1 2 2 2 1 2 1 2 2 1 ) 1 ( ) 1 ( ) ( ds ds ds m ds ds ds ds m s ds ds ds ds mb m out r r r g r r r r g r r r r g g r + + + = + + + = + + + = η ii) Transconductance (when output is shorted to a fixed DC voltage or AC ground) Short the output to an AC ground, and draw the small signal diagram as shown above. According to KCL we can list the following equations, 12 11 23 22 21 i i i i i i out + = + + = (1) where in m gs m v g v g i 1 1 1 11 = = ( 2 a ) 2 1 12 s ds v g i = ( 2 b ) v g2 v in g ds2 v out =0 i 11 =g m1 v gs1 = g m1 v in g ds1 v gs2 v gs1 v s2 v b2 g mb1 v bs1 =g mb1 0=0 v b1 v bs2 v bs1 =0 i 21 =g m2 v gs2 i 23 =g mb2 v bs2 i 22 i out i 12 2 2 2 2 2 2 2 21 ) ( s m s g m gs m v g v v g v g i = = = (2c)
Background image of page 2
S. Yan, EE 338L Lecture 6 3 2 2 2 2 2 2 2 22 ) ( s ds s d ds ds ds v g v v g v g i = = = (2d) 2 2 2 2 2 2 2 23 ) ( s mb s b mb bs mb v g v v g v g i = = = (2e) From Eq. (1), we have ) ( 23 22 21 i i i i out + + = ( 3 a ) Substitute Eqs. (2c)-(2e) into Eq. (3a), we have, 2 2 2 2 23 22 21 ) ( ) ( s ds mb m out v g g g i i i i + + = + + = (3b) From Eq. (1), we have 12 11 23 22 21 i i i i i + = + + ( 4 a ) Substitute Eqs. (2a)-(2e) into Eq. (4a), 2 1 1 2 2 2 2 ) ( s ds in m s ds mb m v g v g v g g g + = + + (4b) Solving Eq. (4b), we get in ds ds mb m m s v g g g g g v 1 2 2 2 1 2 + + + = (5) Substitute Eq. (5) into Eq. (3b), in ds ds mb m ds m in ds ds mb m ds mb m m s ds mb m out v g g g g g g v g g g g g g g g v g g g i + + + = + + + + + = + + = 1 2 2 2 1 1 1 2 2 2 2 2 2 1 2 2 2 2 1 ) ( (6) Thus the transconductance of the cascode amplifier is 1 1 2 2 2 1 1 1 2 2 2 2 2 2 1 1 m ds ds mb m ds m ds ds mb m ds mb m m in out m g g g g g g g g g g g g g g g v i G + + + = + + + + + = = (7) Observation: Compared with a single-transistor common source amplifier with a transconductance of | G m |= g m1 (Note that G m is the transcoducance of the amplifier , and g m is the transcoducance of the transistor ), the transcoductance of cascode amplifier is slightly less, whose transconductance Gm is given by 1 1 2 2 2 1 1 99%) to % 90 ( 1 m ds ds mb m ds m m g g g g g g g G = + + + = .
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
S. Yan, EE 338L Lecture 6 4 iii) DC voltage gain (when the output is open) v g2 v in g ds2 i 11 =g m1 v gs1 = g m1 v in g ds1 v gs2 v gs1 v s2 v
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 17

lecture06 - EE 338L CMOS Analog Integrated Circuit Design...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online